1. Field of the Invention
The present invention relates generally to implantable cardiac stimulation devices and systems for regulating the contraction of a heart. More particularity, the invention relates to a defibrillation lead, and more particularly to a defibrillation lead having a distal electrode and a multi-lumen lead body.
2. Description of the Related Art
Implantable medical devices for treating irregular contractions of the heart with electrical stimuli are well known in the art. Some of the most common forms of such implantable devices are defibrillators and pacemakers.
Defibrillators are implantable medical devices used to treat fibrillation, a condition characterized by rapid, chaotic electrical and mechanical activity of the heart""s excitable myocardial tissue that results in an instantaneous cessation of blood flow from the heart. Defibrillation is a technique employed to terminate fibrillation by applying one or more high energy electrical pulses to the heart in an effort to overwhelm the chaotic contractions of individual tissue sections and to restore the normal synchronized contraction of the total mass of tissue.
A pacemaker, or pacer, is an implantable medical device that delivers low energy electrical pulses to stimulate a patient""s heart to beat at a desired rate in instances where the heart itself is incapable of proper self-regulation. This occurs when the heart""s natural pacemaker, which causes the rhythmic electrical excitation of the heart and pumping of blood, malfunctions due to age or disease. Pacing is a process used to maintain normal beating of a heart having this condition.
Various types of leads for defibrillators and pacers have been suggested in the prior art. For example, large electrical patches sewn to the exterior surface of the heart have been used to deliver defibrillation pulses to the heart. Implantation of such patch electrodes requires opening of the patient""s chest during thoracic surgery. For pacing, pulses may be applied to the heart with the use of a pacer lead having an exposed metal surface, or pacer electrode, extending through a vein and into the heart.
Those involved in the medical arts recognized that prior art defibrillators required a high threshold level of energy for effective defibrillation, which limited the useful life-span of the devices and, more significantly, posed a significant risk of causing electrolysis of the blood and myocardial damage. It was realized that the defibrillation electrode configuration played an important role in the amount of energy needed to achieve successful defibrillation. This led to the development of transvenous defibrillation leads having long coil-shaped defibrillation electrodes for implantation into the right ventricle of the heart through a vein. For example, U.S. Pat. No. 4,922,927, the entire disclosure of which is incorporated herein by reference, discloses a defibrillation electrode made up of a plurality of separate wires wound side-by-side to form a tight coil. The coil was disposed upon an insulated tubular member and had a length sufficient to extend throughout the entire length of the ventricular chamber to provide sufficient electrode surface area for defibrillation.
Transvenous cardiac stimulation leads, such as the device of U.S. Pat. No. 4,922,927, were configured to also carry a pacing electrode. Thus, a single device implantable in one surgical procedure could provide defibrillation and pacing pulses for heart patients suffering from both irregular heart beat and, at times, cardiac fibrillation. This eliminated the need for multiple and complex surgical procedures to attach the prior art electrodes required for both types of treatments.
Another defibrillation electrode configuration for use with dual purpose transvenous leads is disclosed in U.S. Pat. Nos. 5,476,502 and 5,374,287 to Rubin, which are also incorporated herein by reference in their entireties. The xe2x80x9cRubinxe2x80x9d catheter included either a helical or lance shaped defibrillation electrode for delivering a defibrillation pulse directly to the interior of the septum of the patient""s heart. The length of the helix-shaped electrode to be screwed into the septum from the right ventricle, about 0.5 cm to 1.0 cm, was substantially shorter than the conventional coiled transvenous defibrillation electrodes.
Implantable cardiac leads typically have a distal electrode at the extreme distal end of the lead. In cardiac pacemaker leads this electrode is usually a cathodic electrode conducting low voltage pulses which stimulate the heart to contract. Modern endocardial defibrillation leads are now used with devices which provide cardiac pacing as well as defibrillation shock therapy. In such leads, a distal pacing electrode is usually provided, also.
Endocardial defibrillation leads were constructed using co-axial construction typical of pacemaker leads. That is, the lead comprised an outer insulating lead body of silicon rubber or polyurethane with a central lumen. One or more coiled conductors extend through the lumen. These conductors were placed one inside the other and had a common axis with the axis of the lumen in the lead body. The conductors were separated by insulating tubes. The entire assembly was symmetrical around a common axis. Consequently, it was easy to insert an axially symmetrical cathodic electrode at the distal tip.
More recently, defibrillation leads have used lead bodies with multiple lumens, providing additional insulating separation between low voltage and high voltage conductors. Because such lead bodies do not have a lumen symmetrical about the axis of the lead body, it has been difficult to attach the distal electrode, which is typically symmetrical about the lead axis. The most common solution has been to glue a short, tapered tube to the distal end of the lead body. The distal electrode could then be inserted into this tube. This technique expands the diameter of the lead near the distal tip. In addition, It introduces an additional glue joint.
There continues to be a need for improved multi-lumen cardiac leads with distal electrodes which are axially mounted.
In accordance with the present invention, there is provided an implantable endocardial, multi-lumen, defibrillation lead. In the lead of our invention, the distal end of the lead body is cored to provide a stopped bore at the distal end of the lead body. The distal electrode is inserted into the stopped bore without an additional tubular segment and glue joint. A first lumen in the lead body, preferably circular in cross section, has an axis which is off set from the axis of the lead body itself. A low voltage conductor passes through the first lumen. This conductor is preferably a trifilar coil conductor, as is known in the art. A second lumen is also offset from the axis of the lead body. In this embodiment, the second lumen is shown as a non-circular lumen, and contains a looped cable conductor. However, a single cable or a coiled conductor could be used and the second lumen could have a circular or other symmetrical cross section.
In a preferred embodiment, a looped cable conductor conducts high voltage defibrillation shocks. A coil electrode is connected to an elongated, flexible, electrically non-conductive lead body and is supplied with electrical power for delivering electrical shocks to the heart through a looped cable conductor that extends through the lead body and is associated with a power source.
The invention may be used with a pacer and, thus include any of a variety of pacer electrodes and sensors that are presently available or may become available. Such devices would be disposed upon the lead, insulated from the defibrillator electrode segments and electrically connected with a second electrical conductor that extends through the lead body and provides electrical power to the pacer electrode. The lead may also include a ground electrode disposed upon the lead a distance from the other electrodes to receive the pulses delivered to the heart tissue and transmit them back through a third electrical conductor extending through the lead. The coil electrode and looped cable conductor may also serve a dual function as a ground electrode and conductor.
The invention may also be adapted for fixation of the distal end of the lead to the heart to achieve selective positioning of the electrode or electrodes. A variety of currently available passive and active fixation mechanisms, or that may become available, may be used with the invention. In one embodiment of the invention, the lead includes tines. A small fixation screw for securing the distal end of the lead within the heart, wherein the fixation screw also functions as a pacer stimulating and sensing electrode, could be used.
The present invention also provides a system for regulating the beating of a heart. The system includes the lead, as previously discussed, attached to a pulse generator at the proximal end of the lead. In the preferred embodiment, the pulse generator includes a processor, a defibrillator circuit, and a pacer circuit. The processor senses and analyzes the natural electrical charge created by the heart. Depending upon the results of the analysis, the processor informs the pacer circuit or defibrillator circuit to discharge either a pulse or a defibrillation shock, respectively. The pulse then travels down the appropriate electrical conductor and is discharged to the heart through the appropriate defibrillation or pacer electrode.
It is therefore an object of the present invention to provide an endocardial defibrillation lead with multiple lumens and an axially mounted distal electrode. Another object of this invention is to minimize the diameter of a defibrillation lead. It is also an object of this invention to provide methods and apparatus for regulating the beating of a heart. It is another object of the present invention to provide a single apparatus that can effectively deliver both defibrillator and pacer pulses to a heart. Yet another object of the present invention is to provide an apparatus as above that can be inserted in a single surgical procedure. It is yet another object of the present invention to provide an apparatus as above that can be selectively positioned in the heart to target a defibrillator or pacer pulse so as to deliver the defibrillator or pacer pulse to a precisely defined region of the heart.
The characteristics and advantages of the present invention described above, as well as additional features and benefits, will be readily apparent to those skilled in the art upon reading the following detailed description and referring to the accompanying drawings.